L-theanine is an amino acid rich in green tea but otherwise not found in many foods that promotes relaxation by altering the levels of brain chemicals with mood-enhancing effects. Some believe it can promote mental and physical relaxation, decrease stress and anxiety, improve learning performance, heighten mental acuity, and promote concentration; all without inducing drowsiness. A recently published Japanese study examined these possible effects using a mental arithmetic task as an acute stressor. Subjects were exposed to the acute stress task on four occasions using a randomized and balanced procedure. They either took L-theanine at the start of the stress test, half-way through the test, placebo, or nothing. During the L-theanine trials, heart rate and salivary immunoglobulin A (indicator of stress) responses to the stress test were significantly reduced compared to the placebo condition. This is another study showing that L-theanine can help people reduce stress and better relax during stressful situations.

Kimura K, Ozeki M, Juneja LR, Ohira H. L-Theanine reduces psychological and physiological stress responses. Biol Psychol. 2006 Aug 21; [Epub ahead of print]